The shape, size, and distribution of a precipitate and/or an inclusion in a metal sample may greatly affect the characteristics of a material, for example, fatigue properties, hot workability and cold workability, deep drawability, machinability, or electromagnetic properties. A precipitate and/or an inclusion is hereinafter referred to as a precipitate or the like. For example, recent great advances in techniques for improving the characteristics of steel products utilizing a fine precipitate or the like have been associated with the increased precision with which the precipitate or the like is controlled in manufacturing processes.
Representative examples of steel products in which the control of a precipitate or the like is regarded as important include precipitation-hardened high-strength steel. Precipitates or the like contained in this precipitation-hardened high-strength steel sheet have various sizes and compositions. Precipitates can be classified into precipitates that can improve the properties of a steel sheet, precipitates that degrade the properties of a steel sheet, and precipitates that do not affect the properties of a steel sheet. To manufacture high-performance steel sheets, therefore, it is important to stably produce an advantageous precipitate or the like and prevent the formation of a disadvantageous or irrelevant precipitate or the like.
In general, advantages and disadvantages of a precipitate or the like to the properties of a steel sheet are closely related to the size of the precipitate or the like; the strength of a steel sheet increases with decreasing size of a precipitate or the like. Recently, steel sheets strengthened with a nano or subnano precipitate or the like have been developed. To determine the component design and manufacturing conditions of a steel sheet, therefore, it is important to determine the amount and the composition of a precipitate or the like for sizes in a submicron to nano range.
The quantitative determination of extracted precipitates or the like in a steel material has been developed and disclosed basically to evaluate the precipitates or the like as a whole.
The Iron and Steel Institute of Japan, “Tekko Binran, 4th edition (CD-ROM,” Vol. 4, section 2.3.5 describes acidolysis, a halogen method, and electrolysis and reported that electrolysis is particularly suitable for a precipitate or the like. However, electrolysis described in The Iron and Steel Institute of Japan, “Tekko Binran, 4th edition (CD-ROM,” Vol. 4, section 2.3.5 principally aims to aggregate a precipitate or the like in a liquid and recover the precipitate or the like by filtration, that is, to analyze the precipitate or the like as a whole. Thus, the size of the precipitate or the like cannot be determined. Furthermore, by the method described in The Iron and Steel Institute of Japan, “Tekko Binran, 4th edition (CD-ROM,” Vol. 4, section 2.3.5, in a material containing a very small precipitate or the like, the precipitate or the like cannot be sufficiently aggregated, and part of the precipitate or the like passes through a filter. Thus, this method also has a problem with quantitative determination.
As a method for analyzing a chemically extracted non-metallic inclusion in a steel material according to size, Japanese Unexamined Patent Application Publication No. 59-141035 discloses a method for separating and collecting a precipitate or the like having at least a certain size by storing a steel sample placed in an electrolytic bath in a polytetrafluoroethylene net.
Japanese Examined Patent Application Publication No. 56-10083 discloses a technique for separating a precipitate or the like extracted in a liquid by filtration while applying ultrasonic waves to the precipitate or the like to prevent aggregation.
Basically, a precipitate or the like having a smaller particle size has a higher tendency to aggregate in a liquid. In the method described in Japanese Unexamined Patent Application Publication No. 59-141035, therefore, a precipitate or the like aggregates in a liquid in a manner that depends on the particle size. Thus, part of a precipitate or the like having a size smaller than the filter pore size is also trapped. This clearly leads to an inaccurate result of the size-specific analysis. Although aggregation does not cause a significant problem for an inclusion having a target size in the range of 50 to 1000 μm in Japanese Unexamined Patent Application Publication No. 59-141035, a precipitate or the like having a size in a submicron to nano range to which the greatest attention is paid, particularly of 1 μm or less in view of the control of the strength characteristics of steel, more desirably of 200 nm or less, is easily aggregated in a liquid in most cases. Thus, the method described in Japanese Unexamined Patent Application Publication No. 59-141035 is unsuited to practical use.
As in Japanese Unexamined Patent Application Publication No. 59-141035, Japanese Examined Patent Application Publication No. 56-10083 is also directed at a large precipitate or the like having a size of 1 μm or more, which is easy to aggregate and separate. Since the lower limit of sieving is generally 0.5 μm (see Agne Gijutsu Center, “Saishin no Tekko Jotai Bunseki,” p. 58, 1979), the technique of Japanese Examined Patent Application Publication No. 56-10083 is difficult to apply to a precipitate or the like having a size in a submicron to nano range.
Japanese Unexamined Patent Application Publication No. 58-119383 discloses a technique for separating a precipitate or the like having a size of 1 μm or less with an organic filter having a pore size of 1 μm or less under ultrasonic vibration. However, as in Japanese Unexamined Patent Application Publication No. 59-141035 and Japanese Examined Patent Application Publication No. 56-10083, it is impossible to separate an aggregate of a fine precipitate or the like having a size of 1 μm or less with ultrasonic waves.
The Japan Institute of Metals, “Materia,” Vol. 45, No. 1, p. 52, 2006 discloses a technique for extracting a precipitate or the like from a copper alloy and filtering the extract twice through filters having different pore sizes to separate the precipitate or the like according to size. However, the problem relating to aggregation described above is not solved, and part of a precipitate or the like having a size smaller than the filter pore size is also trapped, causing errors in the size-specific analysis results.
As described above, the related art has problems, such as aggregation, and there is no practical and accurate size-specific analysis technique of a precipitate or the like having a size in a submicron to nano range (particularly of 1 μm or less, more desirably of 200 nm or less).
It could therefore be helpful to provide an analysis method in which a precipitate and/or an inclusion, particularly having a size of 1 μm or less, in a metal sample is extracted without loss or aggregation and a size-specific analysis of the precipitate and/or the inclusion is precisely performed.
FIG. 9 shows the extraction procedure of electrolysis disclosed in The Iron and Steel Institute of Japan, “Tekko Binran, 4th edition (CD-ROM),” Vol. 4, section 2.3.5. In that electroextraction, a precipitate or the like in steel can be stably extracted by dissolving an iron matrix. The electroextraction is considered to be a standard method of an extraction analysis of a precipitate or the like (hereinafter referred to as a standard method). Japanese Unexamined Patent Application Publication Nos. 59-141035 and 58-119383 and Japanese Examined Patent Application Publication No. 56-10083 and Agne Gijutsu Center “Saishin no Tekko Jotai Bunseki,” p. 58, 1979 and The Japan Institute of Metals, “Materia,” Vol. 45, No. 1, p. 52, 2006 described above are based on this standard method. However, conventional methods, including the standard method, have various problems, as described above.